Investigation of D�APL Dissolution Kinetics and Interfacial Architecture in a Three- Abstract Abstract #407#407 Poster #Poster #104104

Dimensional Fracture �etworkChristensen, K. 1, Altman, P. 1, King, J. 1, Schaefer C. 2, McCray, J. 1

Partners in Environmental TechnologyPartners in Environmental TechnologyTechnical Symposium & Workshop, Technical Symposium & Workshop, 20082008Christensen, K. , Altman, P. , King, J. , Schaefer C. , McCray, J.

1Colorado School of Mines, Golden Colorado ; 2Shaw Environmental, Inc., Lawrenceville, �JAuthor contacts: kachrist@mines.edu & paltman@mines.edu Analytical Modeling

Relevant Model Equations�The Method of Moments was used to

Purpose� This research is the first to investigate the dissolution behavior of DNAPL in a three dimensional

Experimental Design

Internal DesignExternal Design & Compression System

Relevant Model Equations�The Method of Moments was used tocalculate mass recovered, lineargroundwater velocity, and retardation ofinterfacial tracer.

&

� This research is the first to investigate the dissolution behavior of DNAPL in a three dimensional

fractured sandstone experiment with PCE as the contaminant of interest in this study.

� Accurate characterization of DNAPL architecture and dissolution kinetics in a fractured network

Internal DesignCompression System

Flow

interfacial tracer.�Diffusion tests produced a maximumdiffusion coefficient (D*) and tortuositycoefficient (ω) for the rock matrix.�The CXTFIT analytical transport model

� Accurate characterization of DNAPL architecture and dissolution kinetics in a fractured networksetting yield more efficient application of remedial actions on both the free and dissolved phases infield settings.

�Prior to conducting experiments on PCE dissolution, it is important to fully understand the

Water f low i nput

�The CXTFIT analytical transport modelwas then utilized to determine thehydrodynamic dispersion coefficient andthe mass transfer coefficient.

Data & Results

�Prior to conducting experiments on PCE dissolution, it is important to fully understand thetransport of conservative solutes in our experimental system using conservative tracers (bromideand an anionic surfactant).

Water f low i npu t

the mass transfer coefficient.

Data & Results� Results indicate that dead-end fractures, fractures planes that are outside the primary flowpathway, serve as regions for storage and slow release of solutes, and mimic a dual-domain system.

� The fractured sandstone used in the experimental system has very little matrix porosity therefore,

System Physical Characteristics: 5 cm long by 25 cm wide & 38 cm high

�Dissolution results indicate that 55% of initial NAPL mass emplaced was recoveredduring steady state dissolution at a flow of 4.5 to 6.5 ml/min for 120 days�Stop flow and velocity experiments conducted towards the end of the experiment� The fractured sandstone used in the experimental system has very little matrix porosity therefore,

diffusion into and out of the rock matrix is not a dominant transport mechanism.

5 cm long by 25 cm wide & 38 cm high Flow: 4.0 to 8.5 mL /min

(DNAPL dissolution and fracture characterization )

�Stop flow and velocity experiments conducted towards the end of the experimentresulted in a significant reduction of aqueous PCE concentrations�NAPL distribution plays an important role in dissolution

� The measured mass transfer for the rock matrix

Conceptual Model�APL Distribution in Fracture �etworkExperimental Methods

Continuously monitor and sample effluent for aqueous PCE concentrations

The measured mass transfer for the rock matrixis less than 10-6 cm/min�The mass transfer coefficient (MTC) calculatedby CXTFIT for the tracer tests = 10-4 cm/min.�The two orders of magnitude difference betweenContinuously monitor and sample effluent for aqueous PCE concentrations

Characterize experimental fracture set up

Emplace 200 mLof NAPL into side

ports using syringe & flush with AGW and

Conduct tracer test to

characterize interfacial area

using Br- and

Sample side ports for NAPL using 30 cm needle to

understand NAPL

Maximize flow to flush remaining NAPL, monitor

Conduct tracer test to

characterize interfacial area

using Br- and

�The two orders of magnitude difference betweenMTC calculated using CXTFIT and the measuredvalue (10-6 cm/min) indicates solute transport intoand out of the rock matrix is negligible� Therefore, calculated MTC is attributed to solute

Diffusion Zone - Aqueous phase PCE diffuses out

of dead-end fractures (denoted with red tinting)

and into horizontal fracture/primary flow pathway

fracture set up with conservative tracer test (Br- &

SDBS)

syringe & flush with AGW and have 100 mL

NAPL remain at residual

saturation

interfacial area using Br- and SDBS (SDBS is

non conservative in the presence of

NAPL)

30 cm needle to understand NAPL geometry inside

experimental system

flush remaining NAPL, monitor

effluent and dissolution

interfacial area using Br- and SDBS (SDBS is

non conservative in the presence of

NAPL)

� Therefore, calculated MTC is attributed to solutetransport into and out of the dead-end fractures.

No flow

aqueous zone

Acknowledgements Funding through SERDP project ER-1554

FUTURE RESEARCH� Experiments are planned to investigate DNAPL dissolution kinetics during in situ chemicaloxidation and bioaugmentation will be carried out starting January 2009.

The DNAPL characteristics observed in the 3-D experiment will also be compared to the results

DNAPL

Pooling

Funding through SERDP project ER-1554Dr. John McCray & Dr. Charles Schaefer

� The DNAPL characteristics observed in the 3-D experiment will also be compared to the resultsof analogous experiment performed in a one-dimensional experimental fracture system.